Microphonic relay



Jan. 31, 1939. s. F. LYBARGER MICROPHONIC RELAY 2 Sheets-Sheet l 94. 9u1 S iva/lux m u s. 4.. 6 m n m z la m w m n F '/0 M .lf/M/ A 1 m 6 y.fw 23 Il ,0. 2 a 1 522W ll flu Y n F n if V.. ,h .m B B Jm.31,1939. Is.F. LYBARGl-:R 2,145,603

MIGROPHNIC RELAY x Filed April 26, 1955 2 Sheets-Sheet 2 I VENTOR.

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BYMMMVM fj; ATTORNEYS.

Patented Jan. 3l, 1939 UNITED STATES PATENT OFFICE MICROPHONIC RELAYEdwin JfMyel's 'Application April 2s, 1935, serial No. 18,385

4 Claims.

This invention relates to an improvement in microphonic relays, and moreparticularly to a relay of the amplifier type such as is employed toincrease the amplification in telephonic type 5 hearing aid sets used bypeople with defective hearing.

To satisfy the demands of users of portable hearing aid sets of thisnature it is necessary to make the parts thereof, including theamplifiers,

as small and as inconspicuousas possible, and

also in such a way that they w'ill require a minimum of attention.Because of this and the fact that they must be capable of standing upunder continuous and rather strenuous use their construction becomesconsiderable of a problem. As heretofore made the amplifiers employed inthese sets have embodied several objectionable features. Among the morepronounced of these is the tendency of their operating characteristicsto change with changes in temperature. Another is their tendency to cutout and lose efliciency when oriented to certain positions of rest.Others are their lack of convenient and satisfactory means for adjustingthe air gap between the pole piece and armature of the electromagnetemployed in them and also their inability to respond to a very widerange of frequency impulses as well as their relatively low efficiency.v

With the foregoing in mind it is an object of 3() this invention toprovide an improved amplier of the character referred to which whilesmall and inconspicuous is exceedingly sturdy and simple ofconstruction, dependable and highly sensitive, as well as efficient inoperation and susceptible of being manufactured lat a low cost.

A more particular object is to provide an ampliiier of this type whichwill not cut out in service irrespective of its position of rest.

Another particular object is to provide a relay of this kind with acontinuously adjustable air gap and one in which variations in spacingthereof, due to temperature changes in its armature, are substantiallyeliminated.

A further object is to improve frequency response and flexibilitycharacteristics of sucha relay.

These and Various other objects, as well as the other various novelfeatures and advantages of the invention, will be apparent when thefollowing detailed description is read in conjunction with theaccompanying drawings, of which Fig. 1 is a side elevation; Fig. 2 aplan view; Fig. 3 a front View; Fig. 4 a rear view; Fig. 5 a sectionalView taken on the line V-V of Fig. 2 of a micro- .55 Phonic ampliiierdesigned in accordance with this invention for use in a hearing aid set;Fig. 6 a typical schematic wiring diagram of a hearing aid set showingthe amplifier circuit; Fig. 'l an enlarged fragmentary sectional view ofthe microphone cell in the amplifier showing the dispo- 5 sition of its'carbon spheres when the amplifier is in a vertical position; Fig. 8 aView similar to Fig. 7 but showing the cell disposed in a horizontalposition; Fig. 9 another view similar to Fig. 'l but showing the cellrotated from the posi- 10 tion shown in Fig. 8; Figs. 10, 11 and 12views similar to Figs. 7, 8 and 9 of a modified form of microphone cell;Figs. 13, 14 and 15 views also similar to Figs. 7, 8 and 9 of anothermodified form of the microphone cell; and Figs. 16, 17 and 15 18 likeviews of a still further modification of the microphone cell.

Referring in detail to the embodiment of the invention illustrated inFigs. 1 to 5, the numeral I designates a base plate on which the otherparts 20 of the amplifier are mounted and which is preferably made ofsome suitable insulating composition. On the upper surface of this baseat one end thereof there is mounted a block 2 of cold rolled steel orsimilar material which is em- 25 ployed to function as a part of themagnetic circuit of the electromagnet in the amplifier and also as asupport for various of the other amplilier parts. As shown, this blockis secured to the base I from the under side thereof by a. screw 30 3and a. threaded circuit connecting jack plug 4, and has secured to aprojection 5 on one of its faces by screws 6 an .upwardly extendingarmature 'l and on its other face by screws 8 a similarly disposedhigh-grade bar-type permanent mag- 35 net 9.

At the top of the permanent magnet 9, which is preferably made of cobaltsteel or like material having a high coercive force, there is mounted apole piece II. The latter is made of soft iron o or other highlypermeable material and is employed as a core for a magnetic coil I2. Asshown it is formed in substantially the shape of, or similar to theshape of, a question mark, and is mounted with its curved end fittedover the up- 45 per end of the magnet and its stem portion on which. thecoil I2 is mounted projected toward the armature 'l in parallel relationwith the base plate I. To hold it in place it is secured by screws I3 tothe magnet 9 at a point spaced from 50 the upper end of the magnet. A j

The projection 5 on the block 2 to which the armature 'l is mounted ismade in the shape of the letter L, for a purpose which will presentlyappear, and is disposed with its stem portion F parallel with andslightly above the base I.

The armature 1 which is preferably made of soft iron, silicon steel, orlike material having a high permeability combined with high magneticsaturation point, and in the shape of a flat bar, is secured to the baseI0 of this L-shaped projection 5 and spaced sui'llciently from the polepiece II to provide an adequate air gap therebetween to permit itsnecessary vibratory operation. To readily and'eifectively, as weil asaccurately, adjust this air gap an adjustment screw I4 is threadablyextended through the pole piece II near the upper end of the permanentmagnet 9 with its inner end bearing against such magnet'. Through theuse of this arrangement when the screw I4 is turned in one direction itcauses the curved portion of the pole piece II, which is weaker than thebar magnet 9, to be exed and in such a way that the outer end of thepole piece is drawn away from the armature 1to thereby increase thespacing of the air gap. When it is turned in the opposite direction itpermits the pole piece, due to the latters resiliency, to move towardthe armature and reduce the spacing of the air gap.

The advantage of this adjustment will be appreciated when it isconsidered thatl normally this air gap fin devices of this type ismaintained at from .002 to .003 of an inch and is customarily obtainedby machining the various elements and that their machining to suchaccuracy isy extremely diicult. An error of .0005 of an inch in themachining of any one piece causes an error in spacing of 25 per cent.Furthermore, there is always some variation in the strength of thepermanent magnet 9, in the amount of bending in the armature 1, and inthe spring portion of the armature supporting projection 5. Through theuse of this adjustment the pole Apiece II may be readily adjusted withrespect to the armature over a range of several thousandths of an inch,which makes accurate machining of the parts involved unnecessary, and atthe same time accurate and sensitive adjustment of the air gap isprovided.

At the side of the armature 1 opposite to the magnetic coil I2 amicrophone cell 20 is provided. As shown this comprises a housing I5formed of insulating material which is held in place by a bar I6 securedto the permanent magnet 9 by the same screws that hold the pole piece IIin place, and a pair of rods I1 which are connected between the ends ofthe'bar and the adjacent face of the housing lI5. This bar and theserods are made of some non-magnetic material, such as brass, so as to.not impair the operation of the electromagnet. Through the center of.the housing I5 there is provided acircular chamber forming a hole I8.The outer end of this hole is enclosed by a removable electrode I9 whichis made of carbon or other suitable. material and seated in an'enlargement 2I provided for such purpose at the outer edge of the hole.To hold such electrode in place a resilient current conducting terminaland clamping plate 22 is cmplo'yed being connected by screws 23 to thehousing I5 with its free end bearing against the electrode. y

The inner end of the chamber forming hole I8 in the housing I5 iscovered by a second electrode 24 which is also formed of carbon orsimilar material and soldered or otherwise secured to the adjacent faceof the armature 1. Between thel latter electrode and the housing Ilthere isl allowed a sumcient space to permit the necessary vibration ofthe amature but at the same time insuicient to permit the escape of thecurrent ow regulating material which is placed in the chamber I8. Thematerial that is preferably used for this latter purpose is small carbonspheres having a diameter below 1 millimeter and to prevent their escapethe electrode 24 is spaced from thehousing I5 a-distance which is notgreater than one-half of the diameter of the spheres. If granular carbonis used in place of the spheres, as it may be, as well as other suitablematerial, a loose felt ring or the like, not shown, may be insertedbetween the housing and electrode to prevent its escape.

For connecting the amplier in a headphone and transmitter circuit 25 and26, as well as in a current-supplying battery circuit 21 as shown inFig. 6, four additional jack plugs, 28, 29, 3l and 32 are provided.Three of these, 28, 29 and 3|, are mounted in spaced relation on theupper surface of the base I adjacent the microphone housing I5 and thefourth, 32, is mounted on the bottom of the base adjacent thepreviouslymentioned jack plug 4. Of these, the jack plugs 28 and 29 intowhich the transmitter and headphone circuits 25 and 26 are adapted to beplugged, are preferably of the female type and are connectedrespectively to one end of the electromagnet coil I2 and to thestationary electrode I 9 by current-conducting metallic -strips 33 and34. To secure such strips rigidly in place they are mounted with one enddisposed between the lower end of the plug 28 or 29 and the base. I

and the other attached by a screw to the microphone housing I5.

The two lower jack plugs 4 and 32, which are of the male type andadapted to be plugged into a casing in which the battery circuit 21 iscustomarily housed, are connected respectively to the other end of thecoil I2 and tothe intermediary jack plug 3| which is also of the maletype and used to connect the batteries to the headphone and transmittercircuits 25 and 2B yby way of a current regulating rheostat 35.

As previously stated one of the faults of the prior amplifiersl of thischaracter is that they cut out in service and lose their efficiency whenthey are oriented to different positions. This is due to the falling ofthe Acarbon granules or spheres in the microphone cell away from one ofthe electrodes when they are so oriented. To completely overcome thisdiculty irrespective of the position of the amplifier and to greatlyreduce the loss of efllciency when the amplier is inclined at an angleto the vertical, the electrodes I9 and 24 at the two ends of themicrophone, in accordance with this invention, are made in shapes suchas illustrated in Figs. 7 to 9 and 10 to 12, or, in shapes of thischaracter which give the desired result. As shown in Figs. '1 to 9 thisresult is obtained by providing the electrodes I 9 and 24 with similarlyprojecting centrallyy disposed cone-shaped indents' which insurecontinuous contact between the carbon spheres of the microphone cell andthe electrodes at all times and also a very substantial area of contactin all positions of the 'amplier which makes for eiliciency in theoperation of the cell. This is also true of the cell construction shownin Figs. l0 to-12 where instead of being provided with like disposedconical indents the electrodes are made in the shapes of ilangedhemispheres mounted with their convex portions projecting from theopposite ends of the cell housing.

The customary prior practice has been to make 4 guapos the microphonecell electrodes in the shapes oi' discs, which, as is obvious, allowsthe circuit therethrough to cut out gradually as the cell is canted atan angle to the vertical and completely when the cell is disposed in ahorizontal position as in such position the upper plateis completely outof contact with the carbon spheres. As an improvement upon such practiceonly one of the electrodes may be made as shown in Figs. 13 to 15 and 16to 18 in the shape of the electrodes illustrated in Figs. 7 to 9,- and10 to 12, respectively. While with the latter constructions thecellswill cut out gradually when canted in one direction and completely whendisposed on one side they do so only under such conditions andaccordingly represent a decided improvement over the older type ofconstruction.

As also previously stated, another objectionable tendency of the prioramplifiers is that they change their operating characteristics withtemperature changes. In this respect the armatures have been thechiefsource of evil and such is brought about by the heat generated by thecurrent iowing through the carbon Vcell and the electromagnet coil bothoi which are adjacent the armature and communicate such heat eitherdirectly or indirectly to the amature. In the prior amplifiers as thearmature is heated up by this generated heat it usually moves towardsthe pole piece of the electromagnet and as a result the air gap is madecontinuously smaller the longer the current is on. This of course causesa variation in the sensitivity of the amplifier and under extremeconditions, which are not infrequent, the armature actually touches thepole piece. More frequently, however, it is moved to such an extent thatwhile not in actual contact with the pole pieces it strikes the latterwhen ii i: vibrated by the voice current passed through theelectromagnetic coil I2, and bad distortions are developed in theamplification produced. Such change in spacing of the air gap occurs inall devices Where the armatures are held at two or more positions, asthey customarily have been in the past. In most of the devices theheating of the armature is usually greatest at the point closest to thecarbon cell where the most heat is generated and as a result its lengthis'increased most at such point. If the armature is of the strip typeclamped atboth ends there is considerable movement, due to heat, at thecenter thereof perpendicular to its plane, and as its central portion isnormally displaced slightly from a common plane in which its ends lie bythe permarient magnet as the motion increases the armature moves towardthe pole piece. also true of a circular diaphragm having the armatureattached to it.

In accordance with this invoention the aforementioned difiiculty isovercome by clamping the armature 1 at only one end. As a result thereis no bending in the armature due to heating since all oi' its expansiontakes place in the direction of its length and such expansion in no wayaffects the air gap. While there may be a slight change in thickness ofthe armature due to increases in its temperature this effect isinfinitesimal in comparison to the deleterious effects referred to inthe prior devices. The importance of this phase of the invention will bebest appreciated when it is considered that it insures practicallyconstant sensitivity in the armature regardless of the temperature ofthe armature, or the changes in temperature of the rest of thestructure, as the latter Thisisbecause the horizontal expansion in themounting block is very nearly the same as the horizontal expansion inthe coil. Thus the air gap spacing due to these variables is keptconstant.

Another outstanding feature of the invention resides in the constructionof the armature mounting, the chief advantages of which are that itrenders the amplier responsivel to a wider range of frequencies andadapts it to be readily varied to respond to different frequencies.Another advantage is that by making the armature support capable ofallowing the armature to vibrate and making the armature long tofunction as a lever on its support the varmature can be made heavyenough to properly carry the magnetv ux of the magnetic circuit. Throughthe use of the projection 5 on the block 2 as -a support for thearmature 1 and the armature being secured at only one end, as well asthe base I of the projection having some considerable weight, themounting oi' the armature is not unlike two weights being suspended inseries by separate springs. By reason of this, a mounting is providedwhich has a plurality of natural frequencies which give a maximum ofamplification. With a mechanical structure such as this it can be shownexperimentally and theoretically that as the frequency of thealternating force on the amature, which is produced -by the action ofthe current in the electromagnet, is increased, the amplitude ofvibration of the armature will remain reasonably constant then rise to apoint of maximum vibration or resonance, then decrease until a certainpoint is reached and then increase again to another point of maximumresponse. Thusthe system has two frequencies at which maximum vibrationoccurs and between which there lies a point of less vibration.

The construction asis apparent is one in which the characteristicsreferred to can be readily changed by changing the values of the variouselements comprising the mounting, such as changing the length, thicknessand width of the armature, changing the weight of the screws 6, addingor subtracting weight from the base I 0 of the projection 5, or removingsome of the material from the stem of the projection. A very easy andrecommended method of changing these characteristics is to machine thestem of the projection 5. By doing this, spring action of the projectionis'changed and the thinner it is the weaker its spring action becomes,which makes for a lower first resonant frequency which is desirable.

-In general it is desirable to keep the mass of the armature small toinsure good high frequency response, and to so proportion the elementsof the mounting that the rst resonance or point of maximum vibrationonly is used so that the frequency of minimum vibration is very muchhigher than the highest frequency which it is desired to transmitthrough the amplifier. 'I'he construction recommended is one in whichthe irst frequency of maximum response is between twothirds andthree-fourths of the maximum frequency which it is desired to transmitthrough the amplier. 'I'he actual choice of this frequency, of course,will depend upon the apparatus with which this amplier is used. Theinvention contemplates that a number of different types of constructionwill be provided which have diilferent frequencies of maximum vibrationbel tween 1500 and 4000 ,cycles so that the most suitable ampliioationcharacteristics can be chosen to satisfy the demands of dinerent inydivlduals and as will be obvious and as has been pointed out theconstruction provided is such that it lends itself readily to theprovision' of such a range of devices. y

It will also be appreciated thatthe characteristics lofthisconstruction' atlord'othei advantages.' For example, in many casesin actual practice it is found thatv other parts of the apparatus withwhich it is used, such as the transmitter and headphones, havepronounced resonances or peaks ofy response. By utilizing the fact thata point of minimum response followed by another frequency of maximumresponse is objectionable with this invention, the invention can be usedto advantage to smooth out the over-al1 amplification curve of the jointapparatus by making the' frequency `of minimum response of the ampliiiercoincide with a resonance peak in the associated apparatus., Theover-all response can in this way be made nearly uniform over aconsiderably wider range than is otherwise possible.

'According to the provisions of the patent statutes, I have explainedthe principle and construction of my invention and have illustrated anddescribed what I now consider to represent its4 best embodiment.However, I desire to have it understood that, Within the scope of theappended claims, the invention may be practiced otherwise than asspecically illustrated and described.

I claim:

1. In a microphonic amplier, a supporting base, a block of magneticmaterial secured to said base, a permanent magnet secured at one end toone side of said block, a pole piece adjustably secured to the free endof said magnet, an electromagnetic coil mounted on said pole piece, aflexible projection on the side of said magnetic block opposite to saidpermanent magnet extended in spaced parallel relation to said base, anelongate armature secured at one end to said projection with its freeend disposed in spaced relation thereto opposite the free end of saidpole piece.

2. In a microphonic amplifier, a support, an elongate pole piecedisposed with. an end portion in overlapping engagement with one side ofsaid support, means for rigidly connecting the end of the pole piece tothe support, the projecting portion of the pole piece being providedwith a reverse bend to provide a portion extending along the oppositeside of the support and terminating f armature disposed, a.dj acent thefree end of the pole piece withj an'air gap normallyy between', 5

and 'an adjusting screwimounted izr'saidl over# lappingportion of' thepolepiece and bearing against Atli'ead'loining support for springing thepole piece away from the support to widenjsaid air gap. Y, 1

' 3. In a microphonic amplifier, a support, an elongate pole'pie'cedisposed with an endvportipn in overlapping engagement with one side ofsaid support, means for rigidly connecting 'the end of the pole piecetothe support,'the projecting portion of the pole piece being providedwith a reverse bend to provide a portion'extending along the oppositeside of the support and terminating in a portion extending substantiallyperpendicular to the support, an actuating coil mounted on .1 said lastportion of the pole piece, a block mounted at one side of said coil andprovided with a fiexibie extension substantially parallel to the coilsupporting portion of said pole piece, a

movable armature rigidly connected at one end 2.

to the free endr of said exible extension, the opposite end of thearmature being disposed adjacent the free end of the pole piece with anair gap normally between, and means for springing the pole piece awayfrom its support to vary f said air gap.

4. In an electromagnetic vibrating device for hearing aids, asubstantially straight bar magnet, an elongate pole piece disposed nearone end of the bar magnet with an end portion in overlap- 3- pingengagement with one side of said magnet, means for securingthe end ofthe pole piece to the magnet, the projecting portion of the pole pieceextending substantially at right angles across said end of the Vmagnetin very close proximity thereto and substantially at right angles awayfrom the opposite side of the magnet, an electromagnetic coil mounted onthe free end of the pole piece, a movable armature disposed adjacentsaid freeend with an air gap between them, and an adjusting screwthreadedly mounted in said overlapping portion of the pole piece in veryclose proximity to said end of the magnet against which it bears forspringing the pole piece away from the magnet to, widen said Vair gap.

SAMUEL F. LYBARGER.

